The present invention relates to a headlight for vehicle in accordance with a projection principle.
Headlights of the above mentioned general type are known in the art. One of such headlights is disclosed for example in the German patent document DE 40 02 576 A1. The headlights serves for selectively producing a low beam or a high beam. The headlight has a light source and a reflector for reflecting the light emitted by the light source. A lens is arranged in a beam course of the reflector and a shade device is arranged between the reflector and the lens. The shade device is changeable between a first condition for the operational position of the headlight for the low beam, and a second condition for the operational position for the high beam. The shade device screens in the first condition a part of the light reflected by the reflector and produces a bright-dark limit of the low beam bundle exiting the headlight. In the second condition the shade device shades at least a small part of the light reflected by the reflector. The change of the shade device between its first and second condition can be performed by its movement or the shade device can have at least locally a changeable light permeability, so that the light permeability in the first condition of the shade device is low and in the second condition is high.
The above described known headlight has the disadvantage that it can be optimal either for producing the low beam or for producing the high beam. However, no design is possible for optimal production of both light functions, since the requirements for them are partially contradictory. If the headlight is optimal for the production of the low beam, with the shade device in the first condition, then in the operational position for the high beam with the shade device in the second condition no efficient high beam is produced, since the high beam bundle exiting the headlight can be produced with very low maximum illumination intensities. If to the contrary the headlight is designed so that in its operational condition for high beam with the shade device in its second condition an efficient high beam bundle with its maximum illumination intensities is emitted, then the shade device in its first condition for the operational position of the headlight for low beam must be arranged so that a greater part of light reflected by the reflector is shades, since otherwise the low beam can be produced with impermissibly high illumination intensities. With the arrangement of the shade device required for this in the first condition, moreover substantial image forming error by the lens occurs, such as color edge or over radiation which jointly negatively affects the quality of the low beam bundle. Moreover, the headlight in the operational condition for the low beam is adjusted so that the bright-dark limit assumes the prescribed position, but in the operational position for the high beam the regions with the maximum illumination intensities are located too high.